There is a thermal circuit breaker for the headlights under the dash on 78-80 trucks that can trip and reset itself. Sounds like that is a likely suspect since you've got something else wired in with the headlamps. If you have the fog lamps on a relay, you might go ahead and covert the headlights to run off a relay directly to the battery too. Eliminating the switch and all that extra wiring before the lamps would take load off the circuit breaker and the headlights will shine brighter anyway.
On 77 and older there is a single fuse, headlight switch, that can blow or get flakey and take out all the lights at once.
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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)
MEPR: Man, my 4x4 makes all other LUVs look good
